A reactor chamber as mentioned above is known from European Patent Application EP-247 680, which corresponds substantially to U.S. Pat. No. 4,748,135. Its enclosure has, besides a sample support for a substrate to be treated, a device for introducing gases directly into the hot zone where the sample support is positioned. This device consists of several cylindrical concentric tubes of which the innermost tube issues into one (or several) intermediate tube(s) which issue(s) in its (their) turn into the outermost tube. The latter then ends in the vicinity of a substrate which is to be treated.
The cited application deals exclusively with the problem of introducing the gases into the hot zone of a vapor phase epitaxy reactor.
The problems involved in epitaxial growth in the vapor phase are of a particular nature. On the one hand, the number of samples treated at one time is small. The reactor chambers are accordingly of a small volume.
The problems involved in epitaxial growth are not the same as the problems involved in the heat treatment of wafers of semiconductor material. It should first be realized that the manufacture of integrated circuits comprises steps, such as those of ion implantation, which must be followed by heat treatments at elevated temperatures.
Now certain semiconductor materials, among them the materials of the III-V group, are subject to a change in their surface condition by decomposition when they are brought to the temperatures necessary for carrying out these heat treatments. A solution to this problem consists in a heat treatment which is carried out under a flow of a gas which prevents the change in the surface condition. For example, it is necessary to expose the samples to a flow of arsenic for carrying out the heat treatment of materials for integrated circuits on gallium arsenide. This flow is obtained by cracking of arsine (AsH.sub.3) at elevated temperature in the hot zone of the enclosure of the reactor while the heat treatment is carried out.
The use of gases such as arsine in heat treatments, however, causes a number of problems arising from the characteristics of these gases.
The principal problem lies in the fact that gases obtained in this way by decomposition at high temperature subsequently condense in the cold zones of the chamber on the walls. Such cold zones exist on either side of the hot zone, at either end of the heat-treatment chamber.
Also at the end of the heat treatment, when the sample support is removed from the chamber by translation, for example by means of a rod, the samples necessarily pass through a cold zone in the proximity of the walls polluted by deposition owing to this condensation.
It has thus been found in practice that samples of gallium arsenide of 2 or 3 inches (approximately 5 and 7,5 cm, respectively) diameter could receive more than 20.000 particles per sample.
These deposits of particles owing to the pollution of the cold walls of the heat-treatment chambers are extremely disadvantageous. In fact, they modify to a great extent, unfavorably, the performance of the integrated circuits. They take place on samples which have already been processed for a long time, thus at a stage of manufacture where they have achieved a cost level which is far from negligible. They take place on numerous samples at a time, since the heat treatments are carried out on groups of some fifty samples. In addition, they lead to a spread in the performance of the samples, which thus become less reliable.
Moreover, these deposits remain in the chambers at the end of the heat treatments. It is necessary, therefore, to decontaminate the walls. It is obvious that the samples as well as the contaminated walls constitute a danger for the operators who run the risk of involuntarily inhaling the polluting particles during the final treatment of the samples or during the decontamination treatment of the chamber walls. Especially in the case of, for example, arsine, these polluted particles are highly toxic.
Moreover, the decontamination operation on the chamber walls between each heat treatment is lengthy and costly in terms of manufacturing time.
It is found, accordingly, that the problems involved in the heat treatment of samples under a flow of gases obtained from the decomposition at elevated temperature of polluting compounds capable of condensing at a lower temperature are quite different from those involved in the realization of epitaxial layers. It can be ascertained that these problems gain importance in proportion as the number of samples is higher, the heat-treatment chambers have a greater volume, the quantities of gas involved are greater, the treatment temperatures are higher, and the gases are more toxic.
On the other hand, in other fields of technology where the object is to realize a coating on walls of one portion of an enclosed space to the exclusion of walls in another portion, problems arise when the coating material must be introduced in the form of a gas in obtaining the proper separation between the portion where the coating is to be made and the portion through which the gas is introduced.